clean-up of double zlib files

After including the zlib library sources, zlib.h and zlib.conf are two
times in the project. They should only be inside the zlib folder.
update to zlib 1.2.8

Version 1.2.8 was released on April 28, 2013.
So there is no reason to use an completely outdated version.
updated README

Compiling a static zlib is not necessary anymore.
Merge pull request #57 from EtlamGit/master

zlib update to 1.2.8 and cleanup